Mobile communication devices, for example cellular telephones, may be configured to communicate with more than one type of radio-access network. For example, a device may be capable of attaching to a long term evolution, LTE, network in addition to being capable of attaching to a wideband code division multiple access, WCDMA, and global system for mobile communications, GSM, networks. LTE is an example of a packet-switched only network in the sense that LTE does not support circuit-switched, CS, services such as CS voice.
In compound LTE-WCDMA networks, subscribers may be provided with access to services, such as internet access and messaging. Other services, known as supplementary services, may include call handling such as call forwarding.
In compound networks, one section of the network may be tasked with handling specific services. In an LTE-WCDMA network, for example, services may be provided to users via LTE radio interfaces and WCDMA radio interfaces, separately. Such a compound network may be seen as comprising an LTE radio-access network, a LTE core network, a WCDMA radio-access network and a WCDMA core network. The LTE and WCDMA core networks may be enabled to communicate with each other, in some cases they may even be seen as a unitary core network.
Where a device attached to a packet-switched only network needs to access a circuit-switched service, the device may undergo a network procedure to obtain the service by changing its attachment to a network or interface that supports CS services. In the example of a LTE-WCDMA compound system, a device attached to the LTE radio access network, RAN, may change the attachment interface to WCDMA RAN to obtain a CS service. One procedure for changing attachment to a CS-capable RAN responsive to a determined need to obtain CS service is circuit-switched fallback, CSFB.
Interfaces that support CS service include WCDMA and GSM. Interfaces that are packet-switched only include LTE and wireless local area network, WLAN, interfaces.